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Frequency and Wavelength Calculator

Convert frequency to wavelength and back for light, radio waves and sound, with the period and, for light, the photon energy.

Rules last checked 10 November 2026Every step shown2 sources

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Wavelength

2.9979 m

One cycle lasts
1.000e-8 s
Photon energy
4.136e-7 eV

A 100 MHz electromagnetic wave has a wavelength of 2.9979 m.

How it's worked out

  1. Wave speed299,792,458 m/s (light)
  2. Wavelengthspeed ÷ frequency = 299,792,458 ÷ 1.000e+8 Hz2.9979 m
  3. Photon energyPlanck constant × frequency, in electronvolts4.136e-7 eV
  • Visible light runs from about 380 nm (violet) to 700 nm (red). Radio waves in a cable or glass travel slower than in a vacuum, so their wavelength there is shorter.

How it is worked out

Light and radio waves travel at 299,792,458 m/s in a vacuum. Sound in air travels at about 331.3 + 0.606 × temperature (°C) metres a second. Photon energy is the Planck constant × frequency, shown in electronvolts.

Questions people ask

What is the wavelength of 100 MHz FM radio?

About 3 m: 299,792,458 m/s ÷ 100,000,000 Hz = 2.998 m.

What is the frequency of 500 nm green light?

About 600 THz (5.996 × 10¹⁴ Hz), and each photon carries about 2.48 eV.

What is the formula?

Wavelength = wave speed ÷ frequency, and frequency = wave speed ÷ wavelength.

What speed is used for sound?

The speed of sound in air at the temperature you enter, about 343 m/s at 20 °C.

Formula and rules last checked 10 November 2026Written and tested by the CalculatorDex teamReport a problem

Sources: NIST: Speed of light in vacuum · NIST: Planck constant